Spark plug



Jan. 18, H, M BlCKLE ET AL SPARK PLUG Filed Nov. 29, 1944 Patented Jan. 18, 1949 UNITED STATES PATENT OFFICE -SPARK PLUG 'Harry Milman Bickle, Middlesex, and Ronald Albert Bailey, London, England, a'ssignor, by mesne assignments, to Harry MilmaniBic'kl'e, -Heaton, Middlesex, England A Application November 29, 19.44,"Seria'l No."565;612 4 In'GreatBritain February 2,1944

This invention relates tosparking plugs .for :internal combustion engines, the plugs .being'of the kind comprising a metaltshell or casing :and :an insulator through which the central electrode extends. In plugs of this kind which have heretofore been-in general use onmotorcarengines, the insulator has projected for a considerable distance beyond the outer end of the shell, i. e. the end of the shell remote from the spark gap,

with the result that there is considerable risk of the projecting portion of the insulator becoming damaged, particularly when mounting or dismounting the plug.

The presentinvention has'for one of its objects to provide a generally improved construction of sparking plug inwhich the projecting portion of the insulator may be substantially reduced in length and in whichdangerof a short-circuit 'of the current from the outer end of'the central electrode over the outer surface oflthe insulator hood which has an insulating tubular sleeve'received in the said recess with the central electrode extending within the sleeve, and'm'ean's are provided whereby a 'high tension lead may be electrically connected within the cap or hood to the -central electrode.

The tubular sleeve preferably extends substantiallyto the bottom of therecess in the outerend of the insulator whilstthe capor hood is advantageously formed with a depending skirt whichis spaced from the insulator and which 'extends'into contact with or closely to the outer-end of the metal shell or to the gland nut if one be employed to secure the insulator within the "shell. The central electrode preferably comprisesa plurality of sections, one or more sections being housed within the insulator and one or more sections being housed within the capor hood,'the section or sections housed within the cap or hood being secured thereto so as to be removable with the cap *or hood.

; 'A's'p'arking plug according to anothenasp'ect of 8 Claims. (Cl. 123-169 our invention comprises a metalshell or casing having surfaces for engagement by a box spanner which areso shaped as toallow to the spanner a limited universal movement, the shell or casing being preferably provided with an abutment limiting the extent-to which the plug enters the spanner.

These and otherieatures of our inventionwill 'be:described with reference to the accompanying drawing, in which Fig. '1 is a side -'elevational view, partly in section, of what is now considered to be the preferred form of'sparking plug in accordance Wit our invention;

Fig. 2 is a plan view thereof;

1 Fig. '3 is a'section takenon the line 3-3 of Fig.

, and

Fig. 4 is a partial side elevational view, :drawn to an enlarged scale, of the sparkingplug shown in Fig. 1 afterremoval of the cap and illustrating the limited universal movement permitted to a box spanner shown applied to the shell orcasing.

The sparking plug shown in the drawing comprises an insulator l which, outwardly of the enlargement thereof, has a'substan'tially cylindrical contour and a substantially cylindrical recess 2 extending inwardly from the outer end't'o beyond the outer end of the enlargement. A narrow bore 3 extends from the inner end of the insulator and communicates with the recess 2 by means of a bore 4 which is intermediate in diameter between thenarrow bore 3 and the recess 2 and which is internally threaded. The outer end of insulator I is covered by a cap or hood "5 which is made of any suitable insulating 'material and which 'hasa tubular sleeve 6 which depends centrally from the bas'e'of the cap. In order to prevent excessive flow of heat from the insulator -to the-cap it 'is preferred that the "periphery of the sleeve 8 should be fluted or otherwise suitably 'shapedso'as to give only a limited area of contact with the insulator or that the sleeve should,

as shown, be spaced "from the insulator. The cap or'hoodj has a "dependings'kirt 1 which has an approximately spherical contour and which, together with the base of .the cap, is spaced from the insulator, and the end of the skirt extends into contact with or, vas shown, closely to the outer end of the metal shell '8 within which the insulator 'is' secured in .any suitable manner. In the plugsh'own in the drawing, the outer .end of the shell 8 is .swaged inwardly tosecurethe insulator .to'the shell.

The central electrode comprises two sections, aninner -section "9'wliichis screwed into the intermediate bore E and extends through the narrow bore 3 of the insulator, and an outer section III which is housed in the bore in the sleeve 6 of the cap. The inner section 9 of the central electrode wardly from the inner section 9 of the central electrode. This plug and socket connection not only serves to connect electrically theitwoisections of the central electrode but also to secure firmly the cap in position over the outer end of our inventionthe outerv shell or casing of the the insulator. Preferably the two sections of the central electrode are electrically connected so that they make contact over only a limited area, whereby to limit the transfer of heat from the central electrode to the cap, and in the illustrated embodiment of the invention the plug I3 is throughout most of its length spaced from the wall of socket I2, limited contact with such wall being obtained by means of the spherical enlargement M of the plug. To ensure that the cap is firmly held in position and that good electrical contact is made between plug l3 and the wall of socket l2, the plug is preferably slit longitudinally as shown at It to form two resilient fingers which have to be forced slightly together before the plug can be inserted in the socket. If desired, the wall of socket I2 may be spherically recessed to receive the enlargements Id of the plug in the manner of a snap fastening.

Means are provided whereby a high tension lead may be electrically connected within the cap or hood 5 to the outer section [0 of the central electrode and an advantageous form of such means is shown in the drawing, according to which the base of cap 5 has a bore I! which communicates with the bore in sleeve ,5, this bore I1 extending at any desired angle to the bore in the sleeve 6. Bore I1 is provided with a taper thread and has a circular recess It at the inner end thereof, whilst aspike l9 integral with the outer section [0 of the central electrode extendssubstantially axially of bore ii. To connect the high tension lead to the central electrode, the end portion of the lead, indicated at 20, is screwed into bore l1 until the end of the lead reaches the inner end of the bore. This results in the spike 19 being forced into the conductive core, indicated at 2|, whereby a good electrical connection is made therewith, and also in part of the insulating cover being forced into therecess 18 whereby the high tension lead is firmly secured tothe capor hood.

' The outer section H! of the central electrode is secured within the cap 5 so as to be removable therewith, for example, the cap 5 maybemoulded around the section It, and it will be understood that, once the high tension lead 20 hasbeen se-' cured to the cap,.the lead can be readily connected and disconnected from the plug simply by putting the cap in position on or removingit from the insulator. Since removal of the cap also results in the removal of the upper section In of the central electrode, it will be seen that, with the cap removed, there is no part of the central electrode which projects beyond the insulator and which might be damaged by a spanner applied to the shell. With the cap in position on the outer end of the insulator there is no danger of the hands coming into contact with any part shell at the inner .end-of the inner portions ac.

4 carrying the high tension current and it will be noted that the cap with its depending skirt 1 prevents water or other liquid from entering the recess 2 in the insulator and from causing any short-circuit of the high tension current.

The central: electrode may, ifdesired, include .a series resistor for thepurpose of inhibiting electrode erosion and/or suppressing interference with wireless receiving apparatus. The cap may,

moreover, be provided with a suitable sheet metal screen adapted to be connected to a metallic braid or covering on the high tension cable and also to be earthed through the shell or casing of the plug. r

In accordance with an important feature of the shellor casing illustrated, see more particularlyFig. 4, thepart adapted to be engaged-by thespann'er, is throughout its length of hexagonal section.- The corners of the said parteach comprise an arcuate intermediate portion .sab, thesearcuate intermediate portions lying onaa sphere whose centrev 0 lies on the axis of the shell, and rectilinear inner and outer portions ac and bd which extend tangentially or substantially tangentially to the arcuate portionabu The six spanner-engaging surfaces thus comprisean intermediate portion which is rounded in an axial direction, and plane inner and outer portions which extend at an acute angle to the axis of the shell. It will be Seen that a box spanner 30 may be applied to the shell whilst inclinedto the axis thereof and that the maximum angle of inclination permitted tothe spanner is determined by the angle which the arcuate portions ab subtend at the point 0, the maximum angle of inclination on either side of the shell axis being one half of angle aob. In the shell illustrated in the drawing angle aob is 30f and it will be seenthat the spanner 30 may incline tothe shell axis .at an angle of 15 on either side ofthe axisfi ,In the position of maximum inclination ,the spanner bears on .the shell over a substantial area thereof.

.,-The shellis preferably formed withan annular abutment 22 extending outwardly fromzthe It Will be seen from Fig. 4 that, withthe end of spanner 30 engaging abutment 22, the spanner is'in the position in which it can be inclinedto. the shell axis at the maximum permitted angle of 15.- The abutment 22 thus ensures that-the shell shall not be able-to-enter the spanner to such an extent that the spanner cannot be :inclined at the maximum permiated angle; The abutment 22 has the additional advantage-that it:- prevents the shell from entering: the--spanner to such an extent that the spanner is likely to jamuinthe recess usuallyprovided in the cylinder head. to accommodatethe plug. Although in the, plug shown in the drawing the maximum angle of inclination permitted to the spanner is 15, it will be'understood that the maximum angle of inclination may be more or less than this. The permitted'angle of inclination will generally be governed by the extent to which the insulator projects beyond the shell, being such that there is no danger -of the spanner engaging and damaging the insulator. In the plug according to our invention, since, with the cap removed, there is no part of the central electrode projecting beyond the insulator and the insulator may project for only a short distance beyond the shell, a relatively large angle of inclination may be permitted to the spanner. It will be understood that the part of the shell engaged by the spanner may be, in section, in the shape of a hexagon or other regular rectilineal figure.

We claim:

1. In a sparking plug, a metal shell or casing having a part adapted to be engaged by a box spanner, said part being, in section, in the shape of a regular rectilineal figure, the corners of said part each having an arcuate intermediate portion, the various portions lying on a sphere whose centre lies on the plug axis, and rectilinear inner and outer portions extending substantially tangentially to the arcuate portion of each corner.

2. In a sparking plug, a metal shell or casing having a part adapted to be engaged by a box spanner, said part being, in section, in the shape of a regular rectilineal figure, the corners of said part each having an arcuate intermediate portion, the various portions lying on a sphere whose centre lies on the plug axis, and rectilinear inner and outer portions extending substantially tangentially to the arcuate portion of each corner, said shell or casing also having an abutment preventing the inner end of the spanner from passing beyond the inner end of the said inner rectilinear portions of the corners.

3. A sparking plug comprising a metal shell, surfaces on the shell for engagement by a box spanner which are so shaped as to allow to the spanner a limited universal movement with respect to the axis of the shell, an abutment on the shell limiting the extent to which the plug may enter the spanner, an insulator secured within the shell and having a recess in its outer end. a cap of insulating material covering the outer end of the insulator and having an integral tubular sleeve received in said recess, a skirt depending from the cap and spaced from the insulator, a central electrode comprising a section housed within the insulator and a section secured against removal within the tubular sleeve, means electrically connecting the two sections of the central electrode and removably securing the cap to the insulator, and means for connecting a high tension lead to the said central electrode section mounted within the tubular sleeve.

4. A sparking plug comprising a metal shell, an insulator secured within the shell and projecting beyond the outer end thereof, the insulator having a recess in its outer end, a central electrode secured to and extending through the insulator and into the recess in the outer portion thereof, the portion of the electrode extending into said recess being in spaced relationship to the side wall of the recess, a removable insulating cap covering the outer end of the insulator and having an insulating tubular sleeve projecting into said recess over the portion of the central electrode extending into said recess, a high tension lead within the cap, means for connecting .the high tension lead within the cap to said central electrode, said metal shell having external surfaces therearound forming a polygonal-shaped portion for engagement by a box spanner for mounting and dismounting the sparking plug, the surfaces forming said polygonal-portion being shaped to allow the spanner a universal movement with respect to the axis of the shell, and means for limiting the universal movement permitted to the spanner adapted to prevent its engagement with the outer end of the insulator.

5. A sparking'plug as defined by claim 4 in which the means for limiting the movement of the spanner includes an abutment on the shell inwardly of the polygonal-shaped portion thereof for limiting the extent to which the spanner may be placed over the shell.

6. A sparking plug as defined by claim 4 in which the corners of said polygonal-shaped portion of the shell each have an arcuate intermediate portion, the various arcuate portions lying on a sphere whose center is on the axis of the plug, and rectilinear inner and outer portions extending substantially tangentially to each arcuate portion.

7. In a sparking plug, a metal shell having external surfaces therearound forming a polygonal-shaped portion for engagement by a box spanner used in mounting and dismounting the sparking plug, the surfaces forming said portion being shaped so as to allow the spanner a universal movement with respect to the axis of the shell, and means for limiting the allowable universal movement permitted to the spanner to a predetermined angle with respect to the axis of the shell.

8. In a sparking plug, a metal shell having surfaces for engagement by a box spanner used in mounting and dismounting the sparking plug, said surfaces being so shaped as to permit to the spanner a limited universal movement with respect to the axis of the shell, and an abutment on the shell inwardly of and adjacent the said surfaces for limiting the extent to which the plug may enter the spanner.

HARRY MILMAN BICKLE. RONALD ALBERT BALLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,286,945 Coates Dec. 10, 1918 1,570,320 Serewicz Jan. 19, 1926 1,860,762 Wyrick May 31, 1932 1,927,267 James Sept. 19, 1933 2,080,327 Mascuch May 18, 1937 FOREIGN PATENTS Number Country Date 719/14 Great Britain Sept. 29, 1914 471,331 France Oct. 23, 1914 479,606 Great Britain Feb. 9, 1938 743,521 France Apr. 1, 1933 

